Gas is in the oil on a 2017 Yamaha outboard . How is this happening and what has to be done to fix it. Thanks.
Gas in the oil
Plus one on the rich mixture caused by thermostat open. Unburned fuel washed down the cylinder walls and contaminates the oil.
Normally this is caused by leakage between piston rings and cylinder walls. JMO Using the wrong oil(not recommended), could be part of problem but Rings are also the culprit.
Not an atypical issue. a lot of idling at slow speed can contribute to this as well. Change oil, and run it good and hard. You may see this also posted as "making oil" At low speed the excess fuel can be bled into the crankcase. If I am going to do a lot of slow speed trolling I use the kicker. Other wise I don't put-put along with the 115 Yamaha very much and that seemed to solve my issue.
I had this happen on a 2016 Honda 40 when my uncle used spare automotive oil instead of marine. He didn't think it would make a difference but the engine did NOT agree. Fuel slowly ended up the in crankcase after every use until I noticed it and the dipstick smelled like gas and the oil was very thin. Switched back to Honda factory marine oil and the problem stopped. May not be your solution but something to consider.
First thing to check is your thermostat. A thermostat stuck open will cause your engine to run cold and rich.